An enhancer trap transgenic approach was used to generate these mice. The hsyn-bgi-cre:ERT2-bGHpA transgene was designed with the human synapsin minimal promoter (hsyn) minimal promoter driving a cre-ERT2 fusion gene (cre recombinase fused to a G400V/M543A/L544A triple mutation of the human estrogen receptor ligand binding domain).A beta globin intron separates the promoter from the cre gene and the bovine growth hormone polyadenylation signal follows the cre sequence. This transgene was injected into C57BL/6J embryos. Founder line 1642 was established on a C57BL/6J genetic background.